1. Field of the Invention
The present invention relates to a fixing device of, for example, an electronic copying apparatus for fixing an image transferred to a paper sheet.
2. Description of the Related Art
Generally, a fixing device of this type comprises a heating roller and a pressure roller pressed against the heating roller.
As a paper sheet, with an image transferred thereto, passes between the heating roller and the pressure roller, it is heated and pressurized so that the image is fixed.
The temperature of the heating roller is controlled so as to be constant or variable in two stages, and the pressure roller is pressed against the heating roller under a fixed pressure by means of a spring or the like.
Conventionally, however, the temperature of the heating roller and the pressure loading of the pressure roller are substantially fixed without regard to variations in the temperature and humidity of the outside air. If the outside air temperature falls, or if the outside air humidity increases so that the sheet becomes damp, therefore, the fixing efficiency is liable to be lower than in the normal state.
The fixing efficiency can be improved by increasing the pressure loading of the pressure roller. If the pressure loading is increased too much, however, the paper sheet is subjected to so high a pressure that it will be wrinkled or curled.